How to Grow Four O'Clock Mix From Seed

With their jewel-toned flowers and glossy foliage, four o'clocks (Mirabilis jalapa) add brilliant color and texture to garden beds within U.S. Department of Agriculture plant hardiness zones 8 to 11. They produce an abundance of round, black seeds each year, which can be used to propagate new plants. Four o'clock seeds require no pretreatment and will germinate quickly if you keep them warm and moist. However, they must be handled carefully and kept out of reach of children and pets, because they contain toxic compounds that may cause digestive upset and skin irritation after contact.

Starting Four O'Clock Seeds Indoors

1

Start four o'clock seeds indoors four to six weeks before the last spring frost if you're in an inland area with late-season frost. Fill a 3-inch starter pot with sterile potting mix for each four o'clock plant you wish to grow.

2

Arrange the starter pots on a nursery flat or tray to make handling them easier. Drizzle water into each pot until the potting mix feels moderately moist. Let the excess moisture drain off for 15 minutes before sowing.

3

Sow one four o'clock seed in each starter pot at a depth of 1/4 inch, which is roughly four times the diameter of the seed. Make sure the seed is completely covered, and then gently firm the soil to anchor it.

4

Position the starter pots near a sunny, south-facing window with at least six hours of sunlight daily. Supplement the light with a fluorescent grow light if a naturally bright location is unavailable. Suspend the light roughly 4 inches above the pots for six to eight hours daily.

5

Warm the four o'clock seeds to 70 degrees Fahrenheit using a heating coil or propagation mat. Cover the pots with a large, clear plastic propagation dome to conserve warmth and hold humidity around the seeds. Do not leave heating coils unattended.

6

Check the moisture level in the potting mix every day because it will dry out quickly when exposed to constant heat. Water whenever the potting mix feels nearly dry on the surface. Do not let it dry out completely, or the four o'clock seeds may fail.

7

Watch for the first sprouts in seven to 10 days. Remove the grow lamp and turn off the heating coil once the four o'clock seedlings produce a pair of mature leaves. Continue to water when the potting mix dries out on the surface.

8

Move the four o'clock seedlings to a bright, sheltered location outdoors after the last spring frost. Slowly acclimate them to direct sun and cooler nighttime temperatures over the course of one week -- a process called "hardening off."

9

Transplant the four o'clocks into a permanent bed once soil temperatures warm to at least 65 F. Choose a sunny site with moist, neutral soil. Space them 2 to 3 feet apart and spread a 2-inch layer of mulch between them to protect the roots.

Starting Four O'Clock Seeds Outdoors

1

Start four o'clock seeds outdoors in mild coastal climates or valleys where frosts are rare. Wait until soil temperatures warm to at least 65 F, because the seeds may fail in colder soil.

2

Choose a suitable planting site with full sun exposure, neutral soil and good drainage. Make sure the planting site provides at least 2 square feet of space for each four o'clock plant you're growing.

3

Remove any weeds from the planting site, as well as rocks, sticks and other debris that may inhibit drainage. Till or turn over the top 10 inches of soil. Spray the bed with water to settle the soil.

4

Sow the four o'clock seeds in a grid pattern 6 inches apart, at a depth of 1/4 inch. Make sure the seeds are completely covered with soil. Gently tamp the soil by hand or with the flat side of a hoe.

5

Keep the soil moderately moist in the top 1 to 2 inches while the four o'clock seeds germinate. Watch for the first sprouts in seven to 10 days if daytime temperatures stay reliably above 70 degrees.

6

Thin the four o'clock seedlings to one every 12 to 24 inches. Remove the weakest, least developed seedlings and keep those with a strong stem and healthy looking leaves.

7

Spread a 2-inch layer of mulch between the four o'clocks to protect their new roots and to conserve soil moisture. Water to a 1-inch depth each week during their first summer so they establish a productive root system.

Things You Will Need

3-inch starter pots

Sterile potting mix

Nursery flat or tray

Fluorescent grow lamp (optional)

Heating coil

Propagation dome

Mulch

Tip

Four o'clocks may aggressively self-seed and become invasive in frost-free areas, so be sure to deadhead the spent flowers to prevent unwanted seed production.

Warning

Four o'clock seeds may provoke an allergic reaction when handled, or gastrointestinal distress if consumed.

About the Author

Anastasia Leon began writing professionally in 2001. Her experience as a horticulturalist and nurseryman informs her work, which has appeared in publications such as Mother Earth News and Modern Farmer. Leon is a certified master gardener and holds a Bachelor of Arts from the University of California, Santa Cruz.